Low noise amplifier with constant input impedance

ABSTRACT

A low noise amplifier includes an input transistor, an inductor, and a current sink. The input transistor includes a gate, a drain, and a source, wherein the gate of the input transistor is operably coupled to receive an input radio frequency (RF) signal. The inductor includes a first node and a second node, wherein the first node of the inductor is operably coupled to a power supply and the second node of the inductor is operably coupled to the drain of the input transistor to provide an output of the low noise amplifier. The current sink includes a first node and a second node, wherein the first node of the current sink is operably coupled to the source of the input transistor and the second node of the current sink is operably coupled to a circuit ground, wherein a real component of input impedance of the low noise amplifier is substantially constant when the low noise amplifier is in the off mode as when the low noise amplifier is in the on mode.

This patent application is claiming priority under 35 USC §120 as acontinuing patent application of patent application entitled LOW NOISEAMPLIFIER WITH CONSTANT INPUT IMPEDANCE, having a filing date of Mar.16, 2004, and a serial number of Ser. No. 10/802,016 now U.S. Pat. No.7,110,742.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to wireless communication devices andmore particularly to radio interfaces of such wireless communicationdevices.

2. Description of Related Art

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or channels (e.g., one of the pluralityof radio frequency (RF) carriers of the wireless communication system)and communicate over that channel(s). For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station (e.g., for cellular services) and/or anassociated access point (e.g., for an in-home or in-building wirelessnetwork) via an assigned channel. To complete a communication connectionbetween the wireless communication devices, the associated base stationsand/or associated access points communicate with each other directly,via a system controller, via the public switch telephone network, viathe Internet, and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the transmitter includes a datamodulation stage, one or more intermediate frequency stages, and a poweramplifier. The data modulation stage converts raw data into basebandsignals in accordance with a particular wireless communication standard.The one or more intermediate frequency stages mix the baseband signalswith one or more local oscillations to produce RF signals. The poweramplifier amplifies the RF signals prior to transmission via an antenna.

As is also known, the receiver is coupled to the antenna and includes alow noise amplifier, one or more intermediate frequency stages, afiltering stage, and a data recovery stage. The low noise amplifierreceives inbound RF signals via the antenna and amplifies then. The oneor more intermediate frequency stages mix the amplified RF signals withone or more local oscillations to convert the amplified RF signal intobaseband signals or intermediate frequency (IF) signals. The filteringstage filters the baseband signals or the IF signals to attenuateunwanted out of band signals to produce filtered signals. The datarecovery stage recovers raw data from the filtered signals in accordancewith the particular wireless communication standard.

In many wireless applications, a radio transceiver includes one antennathat is shared by the receiver section and the transmitter section. Thesharing of the antenna may be achieved by a transmit/receive switch or atransformer balun. In recent advances in the wireless communication art,a transformer balun has been implemented on-chip with the receiversection and the transmitter section. In such an implementation, asingle-ended winding of the transformer balun is operably coupled to theantenna, a first differential winding of the transformer balun isoperably coupled to the receiver section, and another differentialwinding of the transformer balun is operably coupled to the transmittersection.

While the benefits of using an on-chip balun are many, there are someissues of concern, which include impedance matching of the loads on thesingle-ended winding and on the differential winding, efficient energytransfer from the transmitter section to the antenna via the transformerbalun, and complexity of implementation. Such issues arise, at least inpart, due to the loading of the transformer balun varies depending onwhether the transceiver is in a transmit mode or in a receive mode. Forexample, the output impedance of the power amplifier, which is a load onthe differential winding, varies depending on whether the poweramplifier is active or inactive. Further, the input impedance of the lownoise amplifier, which is a load on the differential winding, varies bya factor of two or more depending on whether the low noise amplifier isactive or inactive.

FIG. 1 is a schematic block diagram of a known low noise amplifier(LNA), which exhibits a variable input impedance. As shown, the LNAincludes a differential architecture wherein a differential RF signal isreceived at the LNA inputs N and P and produces a differential output atLNA OUT N and P. When the LNA is active, the input impedance of the LNAis based on the transconductance (gm) of the input transistors, theparasitic capacitance of the input transistors, and the seriesinductance between the source of the input transistors and ground, whichmay be a separate inductor or parasitic inductance of the coupling. Whenthe LNA is inactive, its input inductance is based on the parasiticcapacitance and the series inductance. As such, the input impedance ofthe LNA varies significantly depending on whether the LNA is active orinactive.

Therefore, a need exists for a low noise amplifier that has asubstantially constant input impedance regardless of whether it isactive or inactive such a radio front end may provide efficient energytransfer from the transmitter section to the antenna, provide enhancedimpedance matching, and reduce the complexity of implementation.

BRIEF SUMMARY OF THE INVENTION

The low noise amplifier having a substantially constant input impedanceof the present invention substantially meets these needs and others. Inone embodiment, a low noise amplifier includes an input transistor, aninductor, and a current sink. The input transistor includes a gate, adrain, and a source, wherein the gate of the input transistor isoperably coupled to receive an input radio frequency (RF) signal. Theinductor includes a first node and a second node, wherein the first nodeof the inductor is operably coupled to a power supply and the secondnode of the inductor is operably coupled to the drain of the inputtransistor to provide an output of the low noise amplifier. The currentsink includes a first node and a second node, wherein the first node ofthe current sink is operably coupled to the source of the inputtransistor and the second node of the current sink is operably coupledto a circuit ground, wherein a real component of input impedance of thelow noise amplifier is substantially constant when the low noiseamplifier is in the off mode as when the low noise amplifier is in theon mode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a prior art low noise amplifier(LNA);

FIG. 2 is a schematic block diagram of a wireless communication systemin accordance with the present invention;

FIG. 3 is a schematic block diagram of a wireless communication devicein accordance with the present invention;

FIG. 4 is a schematic block diagram of an embodiment of a low noiseamplifier in accordance with the present invention;

FIG. 5 is a schematic block diagram of another embodiment of a low noiseamplifier in accordance with the present invention;

FIG. 6 is a schematic block diagram of yet another embodiment of a lownoise amplifier in accordance with the present invention;

FIG. 7 is a schematic block diagram of a further embodiment of a lownoise amplifier in accordance with the present invention; and

FIG. 8 is a schematic block diagram of a still further embodiment of alow noise amplifier in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a schematic block diagram illustrating a communication system10 that includes a plurality of base stations and/or access points12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 3.

The base stations or access points 12-16 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12-16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its area. Typically, thewireless communication devices register with a particular base stationor access point 12-14 to receive services from the communication system10. For direct connections (i.e., point-to-point communications),wireless communication devices communicate directly via an allocatedchannel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. The radio includes a highlylinear amplifier and/or programmable multi-stage amplifier as disclosedherein to enhance performance, reduce costs, reduce size, and/or enhancebroadband applications.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processingmodule 64, an analog-to-digital converter 66, a filtering/gain module68, an IF mixing down conversion stage 70, a low noise amplifier 72, aradio front end 85, a local oscillation module 74, memory 75, a digitaltransmitter processing module 76, a digital-to-analog converter 78, afiltering/gain module 80, an IF mixing up conversion stage 82, a poweramplifier 84, and an antenna 86. The antenna 86 is shared by thetransmit and receive paths via the radio front end 85.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions' include, but arenot limited to, scrambling, encoding, constellation mapping, modulation,and/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11 Bluetooth, et cetera) toproduce digital transmission formatted data 96. The digital transmissionformatted data 96 will be a digital base-band signal or a digital low IFsignal, where the low IF typically will be in the frequency range of onehundred kilohertz to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignal prior to providing it to the IF mixing stage 82. The IF mixingstage 82 converts the analog baseband or low IF signal into an RF signalbased on a transmitter local oscillation 83 provided by localoscillation module 74. The power amplifier 84 amplifies the RF signal toproduce outbound RF signal 98, which is provide to the antenna 86 viathe radio front end 85, where the antenna 86 transmits the outbound RFsignal 98 to a targeted device such as a base station, an access pointand/or another wireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the low noise amplifier 72 via the radio front end 85. Thelow noise amplifier 72, which has a substantially constant inputimpedance and will be discussed in greater detail with reference toFIGS. 4-8, amplifies the signal 88 to produce an amplified inbound RFsignal. The low noise amplifier 72 provides the amplified inbound RFsignal to the IF mixing module 70, which directly converts the amplifiedinbound RF signal into an inbound low IF signal or baseband signal basedon a receiver local oscillation 81 provided by local oscillation module74. The down conversion module 70 provides the inbound low IF signal orbaseband signal to the filtering/gain module 68. The filtering/gainmodule 68 filters and/or gains the inbound low IF signal or the inboundbaseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signalfrom the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 2 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the digital receiver processing module 64, thedigital transmitter processing module 76 and memory 75 may beimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiver andtransmitter processing modules 64 and 76 may be a common processingdevice implemented on a single integrated circuit. Further, the memory52 and memory 75 may be implemented on a single integrated circuitand/or on the same integrated circuit as the common processing modulesof processing module 50 and the digital receiver and transmitterprocessing module 64 and 76.

FIG. 4 is a schematic block diagram of a low noise amplifier (LNA) 72that includes an input transistor T_(IN), and inductor L_(I) and acurrent source (CS). The input transistor is operably coupled to receivean RF signal 88 and amplify it based on the inductor, the properties ofthe transistor T_(IN), and the current being sinked by the currentsource. The output of the low noise amplifier is provided at the nodecoupling the drain of the input transistor T_(IN) to the inductor. Sucha low noise amplifier is configured for single-ended signals andprovides a substantially constant input impedance whether the wirelesscommunication device is in a transmit or receive mode, where the LNA isoff in the transmit mode and is enabled in the receive mode. The valuesof the inductor and current sinked by the current source will varydepending on the desired output power and frequency of the RF signal.For example, the inductor L_(I) may range from hundredths ofnano-henries to tens of nano-henries and the input transistor may rangein a width length ratio of 50 microns/0.065 microns to 150 microns/0.26microns.

FIG. 5 is a schematic block diagram of another embodiment of a low noiseamplifier 72. In this embodiment, the low noise amplifier 72 includesinductor L₁, a cascode transistor T_(CASCODE), the input transistor, thecurrent source (CS), an adjustable capacitor C_(ADJ) and an inputcapacitor C_(IN). The cascode transistor is bias via a bias voltageV_(BIAS), where the low noise amplifier output (LNA_(OUT)) is providedat the node coupling the inductor to the cascode transistor.

The RF signal 88 is operably coupled to the input transistor via theinput capacitor C_(IN). To adjust the input impedance, the adjustablecapacitor C_(ADJ) is adjusted based on an input selection signal 100. Inthis embodiment, the input capacitor in series with the parallelcombination of the parasitic capacitance of the input transistor and theadjustable capacitor provide the input impedance of the low noiseamplifier when the LNA 72 is enabled. Note that, in the on state, thecurrent source appears as a short circuit for high frequency signalanalysis. In the off state of the LNA, the input capacitor in serieswith the parallel combination of the parasitic capacitance of thecurrent source, the parasitic capacitance of the input transistor, andthe input capacitor provide the input impedance of the low noiseamplifier.

In this embodiment, the adjustable capacitor provides a 1^(st)capacitance value based on the impedance selection signal when the lownoise amplifier is in the off-mode and provides a 2^(nd) capacitancevalue based on the impedance selection signal 100 when the low noiseamplifier is in the on-mode such that an imaginary component of the lownoise amplifier input impedance is substantially constant regardless ofwhether the low noise amplifier is in the on-mode or off-mode.

As one of average skill in the art will appreciate, the input impedanceof low noise amplifier 72 includes a real component and an imaginarycomponent. With the various configurations of FIGS. 4-8, the realcomponent of the input impedance of the low noise amplifier remainssubstantially constant regardless of whether the low noise amplifier isin the on-mode or off-mode. To ensure that the imaginary component ofthe input impedance of the low noise amplifier remains substantiallyconstant, the adjustable capacitor is adjusted.

FIG. 6 is a schematic block diagram of another embodiment of a low noiseamplifier 72 that operates on a differential RF signal 88. In thisembodiment, the low noise amplifier includes two output inductors L₁ andL₂, two bias transistors T_(BIASN) and T_(BIASP), to input transistorsT_(INN) and T_(INP), two input capacitors C_(INN) and C_(INP), twoadjustable capacitors C_(ADJN) and C_(ADJP), and two current sources CSNand CSP. The adjustable capacitors C_(ADJN) and C_(ADJP) are adjustedbased on the impedance selection signal 100 to ensure that the imaginarycomponent of the input impedance of the low noise amplifier remainssubstantially constant regardless of whether the low noise amplifier ison or off.

FIG. 7 illustrates another embodiment of a low noise amplifier 72. Inthis embodiment, the low noise amplifier includes the output inductorL₁, the bias, or cascode, transistor T_(BIAS), the input transistorT_(IN), the current source, an input bias resistor R, and the inputcapacitor C_(IN). The current source includes a sink transistor T_(SINK)and a current mirror. In this embodiment, the input impedance of the lownoise amplifier 72 is more clearly represented in that the currentsource includes the sink transistor. The parasitic components of thesink transistor contribute to the input impedance. The adjustablecapacitor, (not shown) may be added to compensate the imaginarycomponent of the input impedance such that it remains substantiallyconstant in the on and off modes of the low noise amplifier.

Note that the size (width and length) of the bias transistor and theinput transistor may be of the same. Further, the input transistor mayuse a small length to improve the speed of operation. For instance, theinput transistor may have a width length of 96 microns/0.13 microns.

FIG. 8 illustrates yet another embodiment of the low noise amplifier 72.In this embodiment, the low noise amplifier is a differential low noiseamplifier and includes inductors L₁ and L₂ (e.g., 7.38 nH, Q=6.55),input transistors T_(INN) and T_(INP) (e.g., W/L=96 μ/0.13 μ), inputcapacitors C_(INN) and C_(INP), input bias resistors R_(N) and R_(P) andcurrent sources CS-N and CS-P. Note that a single current source may beused in place of CS-N and CS-P operably coupled to ground and thesources of the input transistors. The bias, or cascode, transistorsinclude a plurality of parallel transistors each coupled to a differentcontrol signal. In this embodiment, three transistors are coupled inparallel to the bias transistor and are controlled by control signals A,B, C. Further, three additional transistors are coupled to the source ofthe primary bias transistor and are gated by the inverse signals of A, Band C. The drains of each of these additional transistors are coupled tothe power supply (V_(DD)).

In this embodiment, the cascode transistor configuration allows fordifferent level shifting of the low noise amplifier, and/or differentpower levels of the low noise amplifier.

As with the previous embodiments of the low noise amplifier, thisembodiment provides a substantially constant real component of the inputimpedance of the low noise amplifier regardless of whether the low noiseamplifier is in the on-state or off-state. With the addition of theadjust capacitors (not shown), the imaginary component of the inputimpedance of the low noise amplifier may also be adjusted to remainconstant regardless of whether the low noise amplifier is in theon-state or off-state.

As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

The preceding discussion has presented a constant input impedance lownoise amplifier that may be used in a wireless communication device. Asone of average skill in the art will appreciate, other embodiments maybe derived from the teaching of the present invention without deviatingfrom the scope of the claims.

1. A radio frequency integrated circuit (RFIC) comprises: a receiversection, when enabled, converts inbound radio frequency (RF) signalsinto inbound baseband signals, the receiver section including a lownoise amplifier comprising: an input transistor having a gate coupled toreceive the inbound RF signals, a source, and a drain operable toproduce amplified RF signals; an inductor coupled between a power supplyand the drain; and a current sink coupled between the source and acircuit ground, wherein a real component of input impedance of the lownoise amplifier is substantially constant when the receiver section isenabled as when the receiver section is disabled; a transmit section,when enabled, converts outbound baseband signals into outbound RFsignals; and a transformer balun that includes a single-ended winding, afirst differential winding, and a second differential winding, whereinthe single-ended winding is coupled to an antenna, the firstdifferential winding is coupled to the low noise amplifier of thereceiver section, and the second differential winding is coupled to thetransmitter section, wherein loading of the transformer balun issubstantially constant when the receiver section is enabled or when thetransmit section is enabled.
 2. The RFIC of claim 1, wherein thereceiver section further comprises: a down-conversion module coupled toconvert the amplified RF signals into down-converted signals; and afilter/gain module coupled to at least one of filter and adjust gain ofthe down-converted signals to produce the inbound baseband signals. 3.The RFIC of claim 1, wherein the low noise amplifier further comprises:a variable capacitor circuit coupled to the input transistor, whereinthe variable capacitor circuit provides a first capacitance value basedon a first impedance selection signal when the low noise amplifier is inan off mode and provides a second capacitance value based on a secondimpedance selection signal when the low noise amplifier is in an on modesuch that an imaginary component of the input impedance of the low noiseamplifier is substantially constant when the low noise amplifier is inthe off mode as when the low noise amplifier is in the on mode.
 4. Aradio frequency integrated circuit (RFIC) comprises: a receiver section,when enabled, converts inbound radio frequency (RF) signals into inboundbaseband signals, the receiver section including a low noise amplifiercomprising: an input transistor having a gate coupled to receive theinbound RF signals, a source, and a drain operable to produce amplifiedRF signals; an inductor coupled between a power supply and the drain;and a current sink coupled between the source and a circuit ground,wherein a real component of input impedance of the low noise amplifieris substantially constant when the receiver section is enabled as whenthe receiver section is disabled; a transmit section, when enabled,converts outbound baseband signals into outbound RF signals; and a radiofront end coupled to the receiver section and the transmit section,wherein loading of the radio front end is substantially constant whenthe receiver section is enabled or when the transmit section is enabled.5. The RFIC of claim 4, wherein the receiver section further comprises:a down-conversion module coupled to convert the amplified RF signalsinto down-converted signals; and a filter/gain module coupled to atleast one of filter and adjust gain of the down-converted signals toproduce the inbound baseband signals.
 6. The RFIC of claim 4, whereinthe low noise amplifier further comprises: a variable capacitor circuitcoupled to the input transistor, wherein the variable capacitor circuitprovides a first capacitance value based on a first impedance selectionsignal when the low noise amplifier is in an off mode and provides asecond capacitance value based on a second impedance selection signalwhen the low noise amplifier is in an on mode such that an imaginarycomponent of the input impedance of the low noise amplifier issubstantially constant when the low noise amplifier is in the off modeas when the low noise amplifier is in the on mode.